1. Field of the Invention
The present invention generally relates to constant velocity universal joints. More specifically, this invention relates to constant velocity universal joints and a method for their assembly which more readily facilitates the assembly procedure and which provides a more durable construction.
2. Description of the Prior Art
Constant velocity universal joints are well known in the art and are employed where transmission of a constant velocity rotary motion is desired or required. Constant velocity universal joints typically consist of an inner race, an outer race, a cage which is interposed between the inner and outer races, and a plurality of drive balls which are circumferentially spaced by the cage between the inner and outer race.
The inner race is typically annular in shape and has an exterior surface that is an axially truncated sphere. The exterior surface has a plurality of axially oriented ball tracks which are circumferentially and evenly spaced. Each pair of adjacent ball tracks forms a lobe therebetween whose outer radial surface retains the exterior spherical form of the inner race.
The interior surface of the inner race is generally formed to receive a splined shaft or any other suitable member capable of transmitting rotational motion.
The outer race is also typically annular in shape to receive the inner race. The interior surface of the outer race is spherical in shape and is provided with ball tracks which correspond in number and spacing to the ball tracks of the inner race. Each pair of adjacent ball tracks forms a lobe therebetween whose inner radial surface retains the interior spherical form of the outer race. The exterior surface of the outer race is typically restricted by the envelope that it must reside within.
The cage is also annular in shape and is provided with windows which correspond to the ball tracks of both the inner and outer race. A drive ball is housed within each window and simultaneously engages both an inner and outer race ball track.
In practice the inner and outer race are typically mounted to the adjacent ends of input and output shafts. During operation the cage is dynamically oriented to an attitude in which the plane of the drive balls bisects the angle formed by the intersection of the shafts. The point at which the plane of the drive balls passes through the axis of the cage may be referred to as the theoretical joint center.
To ensure the ease of assembling the inner race with the cage, it is known in the art to circumferentially elongate one or more cage windows to accommodate a lobe of the inner race, as taught in U.S. Pat. No. 1,916,442 to Rzeppa. By this arrangement the axis of the inner race is positioned perpendicular to the axis of the cage and a lobe of the inner race is inserted into the elongated window. This provides sufficient clearance to allow insertion of the diametrally opposing lobe into the cage. The inner race can then be positioned to be centered within the cage and then rotated 90 degress until the inner race and cage are coaxial.
A significant deficiency in this arrangement is the reduced circumferential width of the partitions between the elongated window and adjacent window of the cage. The narrower partitions decrease the strength and life of the cage and, therefore, the assembly. Further, assembly can only be initiated after ascertaining which window or windows are elongated and then inserting an inner race lobe into that window.
Others in the prior art have attempted in various ways to reduce the resultant stress induced on the cage. U.S. Pat. No. 3,324,682 to Bendler taught an inner race having an axially narrowed lobe. The narrowed lobe allowed the length of the elongated window to be reduced in comparison to the prior art. Bendler taught that it was highly detrimental to narrow all of the lobes of the inner race since it would greatly reduce the contact area between the inner and outer race. However, this restriction complicated manufacturing and assembly by making it necessary to manufacture only one or two narrowed lobes, and then establish which lobe was narrowed before initiating assembly. Further, it is apparent that Bendler still resulted in a weakening of the cage, although less than the prior art.
U.S. Pat. No. 3,412,480 to Cull approached the problem by increasing the cage section adjacent to the elongated windows. Cull retained the elongated windows but increased the axial width of the elongated window's outer axial frame. The outer axial frame is that part of the cage which encloses the windows at the axial end adjacent the shaft engaging the inner race. The stress induced by the drive balls being urged toward the outer axial frame was thereby reduced. Again, this configuration would also require ascertaining which window was elongated before assembly could begin.
An alternative method to facilitate assembly taught by U.S. Pat. No. 4,156,353 to Welschof involved reducing the diameter of the inner race towards one axial end. The diameter reduction produced a tapered effect to the lobes of the inner race, overcoming the requirement to elongate the cage windows. However, this method reduces the bearing surface between the inner and outer race. This is an undesirable result as taught by Bendler.
Lastly, U.S. Pat. No. 4,275,531 to Welschof did not teach the assembly of the inner race with the cage, but addressed the assembly of the cage with the outer race. Welschof taught decreasing the outer diameter of the axial end of the cage towards the outer race shaft. Thus, the smaller diameter end of the cage could be inserted first into the outer race to facilitate assembly, yet the wall section upon which the drive balls bear, the axial end towards the inner race shaft, would still be at full section for strength. However, this method did not effect and, consequently, improve assembly of the inner race with the cage.
As can be appreciated from the above, there is a distinct need for a constant velocity universal joint and a method for assembling a constant velocity universal joint which simultaneously provide a durable cage while readily facilitating the assembly procedure.
Accordingly, what is needed is a constant velocity universal joint and an improved method for assembling a constant velocity universal joint which facilitates the assembly of the inner race with the cage but does not require reducing the circumferential width of the partitions between adjacent windows of the cage or significantly reducing the inner race lobe bearing surface.